Membrane filter for water treatment

ABSTRACT

The invention relates to a membrane filter for water treatment, comprising a head piece including a permeate collecting chamber with a permeate outlet, and at least one fiber bundle made from capillary membranes, which are secured into the head piece with an end that is open towards the permeate collecting chamber and sealed on the opposite end thereof. The head piece contains an air duct to which the mouth piece that protrudes into the fiber bundle is connected with at least one air outlet. At its other end, the fiber bundle terminates in freely movable manner in the untreated water.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/354,917, filed Jan. 16, 2009, which is a continuation of U.S.application Ser. No. 11/611,294, filed Dec. 15, 2006, now abandoned,which is a continuation of U.S. application Ser. No. 11/419,054, filedMay 18, 2006, now U.S. Pat. No. 7,160,454, which is a continuation ofU.S. application Ser. No. 10/380,568, filed Aug. 1, 2003, now abandoned,which is a national stage entry of PCT/EP2001/009788, filed Aug. 24,2001, which claims priority to German Application No. 10045227.2, filedSep. 13, 2000, all of which are incorporated herein by reference intheir entirety.

BACKGROUND

A membrane filter having capillary membranes of the membrane filter thatcan be used in immersion operation that are clamped between two headpieces at their ends is known from WO 98/28066. A gasification device isconnected at the one head piece, which is the lower one in operation.The other, upper end contains the permeate collecting chamber. It formsa displacement body, which has the effect of displacing the rising airbubbles towards the outside of the membrane fiber bundle. Effectivegasification is no longer guaranteed in the upper region of the fiberbundle. Here, no membrane movements are possible either, or only slightmembrane movements are possible. As a consequence, the formation ofmembrane cover layers and of gross dirt deposits occurs in the upperregion of the fiber bundle.

In a membrane filter known from DE 198 11 945 A1, the fiber bundle ofcapillary membranes is set into a pressure-resistant mantle pipe,through which the flow passes in the lengthwise direction of thecapillary membranes. The capillary membranes are secured into an in-flowbase at their ends, which base has a plurality of bores uniformlydistributed over its cross-section, to allow the untreated water to flowthrough. In order to prevent cover layers from forming on the outside ofthe capillary membranes, and to prevent the micropores of the capillarymembranes from becoming blocked, a uniform flow through the membranefilter chamber, at a defined flow velocity, is required. In order toimprove the material exchange, the untreated water can be gasified withair before it enters into the membrane filter chamber. Sufficient airdistribution within the fiber bundle is not guaranteed. The air isessentially guided along the outside of the membrane bundle, with theuntreated water flow, and does not make any effective contribution tothe membrane purification effect.

SUMMARY

The invention relates to a membrane filter for water treatment,comprising a head piece including a permeate collecting chamber with apermeate outlet, at least one fiber bundle made from capillarymembranes, which are secured into the head piece with an end that isopen towards the permeate collecting chamber and individually sealed onthe opposite end thereof, and a gasification device with a mouth piecethat has at least one outlet for air and extends essentially parallel tothe capillary membranes, within the fiber bundle, whereby the capillarymembranes of the fiber bundle that are surrounded by the untreated waterto be treated are attached, in a dense packing, to a connecting surfaceof the head piece, and clarified liquid can be withdrawn in thecapillary membranes, to the permeate collecting chamber. The capillarymembranes possess a diameter of less than 5 mm and preferably have thepermeability of microfiltration membranes or ultrafiltration membranes.However, the use of capillary membranes for reverse osmosis ornanofiltration is not supposed to be precluded. Capillary membranes in adiameter range between 0.5 and 3 mm are preferred. The driving force forthe membrane filtration is a pressure difference that can be implementedon the permeate by means of a pressure reduction. A pressure reductionon the permeate side is a particular possibility if the membrane filteris supposed to be used in immersion operation and is suspended in abasin that contains the untreated water, e.g. the activated sludge basinof a sewage treatment plant.

The invention is based on the task of indicating a membrane filter forwater treatment in which effective gasification over the entire lengthof the fiber bundle is guaranteed, and an effective transport to removemembrane deposits that come loose from the membrane surfaces is assured.

This task is accomplished, according to the invention, in that the headpiece contains an air duct to which the mouth piece that protrudes intothe fiber bundle is connected, and that the fibers of the bundleterminate, at their other ends, without being clamped in place, infreely movable manner in the untreated water. The air that exits fromthe mouth piece flows through the fiber bundle from the inside to theoutside, and partially flows away in the lengthwise direction of thecapillary membranes. The air feed is preferably supplied intermittently,with the goal of cleaning off cover layers that have formed on themembrane surface during membrane filtration. The air introduction intothe fiber bundle, according to the invention, allows surprisinglyeffective cleaning, independent of the flow velocity of the untreatedwater. In this regard, the membrane filter according to the inventioncan also be used in immersion operation.

The mouth piece possesses a pipe-shaped section, for example, with boreson the circumference, or is structured as a ring gap nozzle, from whichthe air exits radially or at least with a radial movement component. Theair can be introduced into the fiber bundle in targeted manner by meansof sizing the length of the mouth piece and by the arrangement of theexit bores or exit nozzles. It also proves to be advantageous if themouth piece has a kick-back valve that closes if the pressure of the airfeed drops.

The fiber bundle is attached to a connecting surface of the head piece,in a dense packing; in case of immersion operation of the membranefilter, this connecting surface is not penetrated by flow channels forthe untreated water. The capillary membranes, which are sealed at theirfree ends, move in the untreated water to be filtered, since they areonly clamped in place at one end. To limit the lateral movements of thefiber bundle, a basket can be set onto the head piece around the fiberbundle. The basket can be made of rods or, for example, can consist of apipe that has been provided with openings on its circumference. The headpiece can furthermore have connecting devices for attachment to a frame,which can be lowered into a basin that contains the untreated water. Itlies within the scope of the invention to structure the head piece inblock shape, whereby the permeate run-off takes place at a narrow sidesurface or at the bottom. Several of these units can be arranged next toone another, in the form of a filter package, whereby it is practical ifthe permeate outlets are connected with one another by means of acollecting line.

If the membrane filter is used in immersion operation, no devices arerequired for making the untreated water flow against the capillarymembranes. According to the invention, a fiber bundle is provided thatcontains the capillary membranes in a very dense packing, whereby theuntreated water is guided past the fiber bundle on the outside, and airis introduced within the fiber bundle. Preferably the fiber bundle isarranged vertically in the untreated water in all the embodiments,whereby the capillary membranes are fixed in place on the head piece attheir lower ends, and their upper end can move in the liquid. The airbubbles rise to the top essentially within the fiber bundle, and theyare not entrained, or only entrained to a slight extent, by the liquidon the outside.

In the following, the invention will be explained in greater detail,using drawings that merely represent an exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate membrane filters for water treatment, accordingto the invention, which can be used in immersion operation, inlengthwise cross-section, in each instance.

DETAILED DESCRIPTION

The fundamental structure of the membrane filters according to theinvention as shown in the figures includes a head piece 1, which has apermeate collecting chamber 2 with a permeate outlet 3, and at least onefiber bundle 4 made up of capillary membranes 5, which are sealed at oneend and are secured into the head piece 1 at their other end, with anopen end towards the permeate collecting chamber 2. The capillarymembranes 5 are preferably ultrafiltration membranes or microfiltrationmembranes, the diameter of which is less than 5 mm. Preferably, thecapillary membranes possess a diameter between 0.5 and 3 mm. Thecapillary membranes 5 are surrounded by the untreated water 6 that is tobe treated. Filtration takes place on the basis of a trans-membranepressure difference, which can be generated by means of an excesspressure on the untreated water side and/or by a reduced pressure on thepermeate side. The clarified liquid flows off through the lumen of thecapillary membranes towards the permeate collecting chamber 2 connectedto the open end of capillary membranes 5.

The capillary membranes 5 of the fiber bundle 4 are attached, in a densepacking, to a connecting surface 7 of the head piece, which surface isnot penetrated by flow channels for the untreated water. A gasificationdevice 8, from which air exits, is arranged within the fiber bundle 4.The air feed preferably takes place intermittently, with the goal ofcleaning off cover layers that have formed on the membrane surfaceduring membrane filtration. In the embodiment shown in FIG. 1, thegasification device 8 has a protruding mouth piece 10 provided with atleast one air outlet, which mouth piece extends essentially parallel tothe capillary membranes 5 within the fiber bundle 4, and is connected toan air duct 16 that is arranged in the head piece 1. The mouth piece 10has a pipe-shaped section with bores 11 on the circumference, but canalso be structured as a ring gap nozzle, for example, from which the airexits with a radial alignment. The capillary membranes 5 secured intothe head piece 1 at one end are freely movable at their other, sealedend, and perform more or less marked lateral movements under the effectof the turbulence that prevails in the untreated water and/or the flowsthat occur in the untreated water. To limit the lateral movements, abasket 12 is used, which is formed from rods and rings in the exemplaryembodiment. A pipe that can be provided with perforations can also beused as the basket 12.

In the exemplary embodiment of FIG. 2, it is indicated that the headpiece 1 can be structured as a block-shaped element. In the lengthwisedirection of the head piece 1, a plurality of gasification devices 8 isarranged, in order to introduce air into the fiber bundle 4. The fiberbundle 4 consists of a dense packing of capillary membranes 5. The headpiece 1 is suitable for immersion operation and can have connectingdevices, not shown, for attachment to a frame, which can be lowered intoa basin containing untreated water. The permeate outlet 3 is provided atthe narrow face. In this regard, it becomes clear that a plurality ofthe head pieces 1 can be arranged parallel, next to one another.

1. A method to dislodge fouling materials from external surfaces ofhollow fiber membranes immersed vertically in an open basin containingfeed liquid at a feed liquid pressure, the method comprising the stepsof: a) vertically mounting a plurality of porous hollow fiber membraneshaving fixed lower ends fixed in a head piece and freely moveable sealedupper ends adapted to prevent accumulation of deposits along theexternal surfaces and upper regions of the of the membranes, wherein thehead piece comprises: i) a permeate collecting chamber sealed from thefeed liquid and in fluid communication with the lower open ends of eachof the hollow fiber membranes and opposite the sealed, freely movableupper ends; and ii) a gas duct contained in the head piece and connectedto a mouth piece positioned within and surrounded by the hollow fibermembranes, the mouth piece having at least one outlet for a gas; b)submerging the porous hollow fiber membranes in the head piece into thefeed liquid in the open basin with the porous hollow fiber membranesoriented substantially vertically such that the sealed, freely movableupper ends are free to float within the feed liquid; c) applying apressure less than the feed liquid pressure to the permeate collectingchamber to cause permeate to pass through the pores of the hollow fibermembranes in to the permeate collecting chamber; and d) providingpressurized gas to the gas duct to form bubbles that flow through abundle of hollow fiber membranes from the inside to the outside of thebundle of membranes and partially flow away in the lengthwise direction,to contact external surfaces of the hollow fiber membranes over theentire length of the membranes and remove fouling materials from thehollow fiber membranes independent of the flow velocity of the feedliquid, and to cause the hollow fiber membranes to sway.
 2. The methodof claim 1 wherein the pressurized gas is provided constantly.
 3. Themethod of claim 1 wherein the pressurized gas is providedintermittently.
 4. The method of claim 1 further comprising the step ofproviding a liquid to internal surfaces of the hollow fiber membranes tobackwash the hollow fiber membranes.
 5. The method of claim 4 whereinthe liquid is permeate.
 6. A module for a membrane filter to treatuntreated water contained in a tank or basin at an ambient pressurecomprising: a) a plurality of head pieces arranged adjacent to oneanother, wherein the headpieces are block-shaped elements having aplurality of vertical fiber bundles that are a dense packing ofcapillary membranes having fixed lower ends and sealed, freely movableupper ends adapted to float within the untreated water within the tankor basis and thus prevent accumulation of deposits along externalsurfaces and upper regions of the of the membranes; b) a plurality ofgasification devices arranged to introduce air into the fiber bundles toprovide bubbles that flow through the bundle of capillary membranes fromthe inside to the outside of the bundle of membranes and partially flowaway in the lengthwise direction, move upwardly, and contact thecapillary membranes over the external surfaces and upper regions of themembranes to remove fouling materials from the capillary membranesindependent of the flow velocity of the untreated water; c) a membranesupport connected to the head pieces to limit lateral sway of thecapillary membranes; and d) connecting devices for attachment to a framewhich can be lowered into a tank or basin containing untreated water. 7.The module of claim 6 further comprising a frame for immersing theplurality of head pieces into the tank or basin.
 8. The module of claim6 wherein the capillary membranes are packed relative to one another soas to produce a rubbing effect between the membranes when moved.
 9. Themodule of claim 6 wherein the bubbles are provided constantly.
 10. Themodule of claim 6 wherein the bubbles are provided intermittently.